Social Security Disability Insurance (SSDI) is an essential lifeline for millions of Americans. Without it, many families would be in deep financial distress. SSDI is insurance that workers pay for through premiums deducted from their pay. In return, workers gain the right to monthly benefits if a disabling condition ends their capacity to earn a living. This insurance function of SSDI is critically important. The need for it is not made obsolete by the Americans with Disabilities Act (ADA) or by advances in medicine and assistive technology. Such developments expand opportunities for some people with disabilities. But others with disabilities face increasing impediments to work as the demands of work change. Most people with disabilities do not receive SSDI. Some work despite their conditions; others do not meet the strict test of disability for SSDI. Broadly speaking, the goals of national disability policy are to fully integrate people with disabilities into all aspects of American society--including equal opportunity, independent living, and economic self-sufficiency. These goals are pursued through varied systems that provide access to health care, appropriate education, rehabilitation, legal protections against discrimination, and wage replacement income when work incapacity strikes. The SSDI program provides vital income support for workers who have lost their capacity to earn a living. It sustains millions of families and keeps many of them out of poverty. Its policies require a careful balance of security for people who are unable to work and opportunity for those who aspire to work. Lawmakers need to allocate adequate resources for attentive and prompt administration of the program. The fundamental structure of SSDI remains sound and is critically important in today's highly competitive labor market. (Contains 1 table and 1 figure.)